Optical switching plays an important role in telecommunication networks, optical instrumentation, and optical signal processing systems. Optical switches can be used to turn the light output of an optical fiber on or off with respect to an output fiber, or, alternatively, to redirect the light to various different fibers, all under electronic control. Optical switches that provide switchable cross connects between an array of input fibers and an array of output fibers are often referred to as xe2x80x9coptical cross-connects.xe2x80x9d Optical cross-connects are a fundamental building block in the development of an all-optical communications network.
There are many different types of optical switches. One general class of optical switches may be referred to as xe2x80x9cbulk optomechanical switchesxe2x80x9d or simply xe2x80x9coptomechanical switches.xe2x80x9d Such switches employ physical motion of one, or more, optical elements to perform optical switching. An optomechanical switch can be implemented either in a free-space approach or in a waveguide (e.g., optical fiber) approach. The free-space approach is more scalable compared to the waveguide approach.
In optomechanical switches employing the free space approach, optical signals are switched between different fibers by a number of different methods. Typically, these methods utilize selective reflection of the optical signal off of a reflective material, such as a mirror, into a fiber. The optical signal passes through free space from an input fiber to reach the mirror, and after reflection, passes through free space to an output fiber. The optical signals are typically collimated in order to minimize coupling loss of the optical signal between an input and output fiber.
Micro-Electro-Mechanical Systems or MEMS are electrical-mechanical structures typically sized on a millimeter scale or smaller. These structures are used in a wide variety of applications including for example, sensing, electrical and optical switching, and micron scale (or smaller) machinery such as robotics and motors. MEMS structures can utilize both the mechanical and electrical attributes of material to achieve desired results. Because of their small size, MEMS devices may be fabricated utilizing semiconductor processing methods and other microfabrication techniques such as thin film processing and photolithography. Once fabricated, the MEMS structures are assembled to form MEMS devices.
MEMS structures have been shown to offer many advantages for building optomechanical switches. Namely, the use of MEMS structures can significantly reduce the size, weight and cost of optomechanical switches. The switching time can also be reduced because of the lower mass of the smaller optomechanical switches.
Movable MEMS structures are capable of oscillating uncontrollably if they are not damped. Such oscillation is due to MEMS structure design and/or fabrication. For example, very low friction in the hinges of MEMS structures allows them to move easily and repeatedly bounce off of stationary objects such as motion stops. Known methods for damping MEMS structures do not provide quick and efficient damping for all types of structures. Thus, there is a need for a method and/or apparatus that provides quick and efficient damping of MEMS structures.
In one implementation, a method for operating a plurality of MEMS devices including applying a magnitude of a selected actuation signal equal to a first substantially constant magnitude to an actuator to cause a movable structure to begin to accelerate from a first position to impact a motion stop at a second position. The method also includes decreasing the magnitude of the selected actuation signal in a first manner. The method further includes varying at least one of a start time and a duration of the decreasing magnitude of the selected actuation signal and observing a settling time of the movable structure in response to the step of varying. In some implementations, the method includes ascertaining a range of values for the start times and the corresponding durations for each of the plurality of MEMS devices that are capable of providing settling times of the movable structure in conformance with a predetermined specification based on the steps of varying and observing. Such an implementation can further include using the ascertained range of values for each of the plurality of MEMS devices and the selected actuation signal for determining an operating start time and a corresponding operating duration to construct an operating actuation signal capable of providing a settling time for each of the plurality of MEMS devices in conformance with the predetermined specification. In certain implementations, the method also can include controlling a signal source with a programmed processor to selectively apply the operating actuation signal to the plurality of MEMS devices.